The Bering Strait is a narrow passage separating Russia’s Chukchi Peninsula and Alaska’s Seward Peninsula, connecting the Pacific Ocean to the Arctic Ocean’s Chukchi Sea. It serves as a gateway for water, heat, and ice entering the Arctic basin. The Bering Strait does experience an annual freeze cycle, but the ice cover is not always complete or consistent across the entire strait. The formation of sea ice in this region is a complex seasonal phenomenon influenced by dynamic ocean currents and its specific geographic characteristics.
The Annual Freeze Cycle
Sea ice formation typically begins in the northern Bering Sea around late October or November, when ocean temperatures drop to the freezing point for saltwater, which is about -1.7°C. This ice is primarily seasonal sea ice, meaning it forms each winter and melts completely in the summer. The sea ice can remain in the region until the breakup usually begins around May and is complete by June of the following year.
During the peak winter months, the shallower coastal areas and the northern reaches of the strait reliably freeze, often forming shorefast ice that is attached to the coast. The central, deepest parts of the strait, however, often remain ice-free, or contain broken ice floes that are constantly moved by winds and currents. This seasonal ice cover historically makes the strait impassable for non-ice-reinforced surface vessels. The timing and extent of the ice cover are highly variable from year to year, often associated with warmer air and water temperatures and southerly wind patterns.
Geographic and Oceanographic Factors
The physical characteristics of the Bering Strait dictate the nature of its freezing. The strait is shallow, with an average depth of 30 to 50 meters. This relatively shallow depth facilitates faster cooling of the entire water column during the cold winter months, which promotes ice formation.
The strait is also a major conduit for the northward flow of warmer, less-saline Pacific Ocean water into the Arctic. This current acts as a significant source of heat transport, inhibiting freezing in the central areas. The heat transported through the strait can account for a substantial percentage of the sea ice loss in the Pacific sector of the Arctic. While the flow is predominantly northward, strong winds can temporarily reverse the current, affecting the transport of both water and ice.
Climate Change and Ice Variability
Over recent decades, long-term trends have shown a significant reduction in the overall sea ice coverage in the Bering Strait region, with the duration of the freezing season becoming shorter. The years 2018 and 2019, for example, saw extreme minimum sea-ice years, attributed to a combination of background warming and specific extreme weather events. The ice that does form is increasingly “first-year ice,” which is thinner and less resilient than the older, thicker ice that was once more common.
The observed loss of sea ice is a self-reinforcing process. Less ice means more open water that absorbs solar heat, leading to warmer ocean water and further reduction in ice formation. This has resulted in longer open-water periods for the regional marine ecosystem. The future environment of the Bering Strait will be defined by this underlying warming trend, coupled with large interannual variability and an increased frequency of extreme weather events.
Impact on Shipping and Wildlife
The changing ice conditions have consequences for both human activity and the environment. For shipping, the loss of sea ice has made the strait more accessible for commercial vessels, particularly as a potential gateway to the Northern Sea Route. This trend has led to a notable increase in vessel traffic, with the number of ships transiting the Bering Strait nearly doubling in a recent decade.
Consequences for Shipping
Increased shipping brings associated risks, including oil spills, greater underwater noise, and the potential for ship strikes on marine mammals.
The reduction in sea ice coverage directly affects ice-dependent wildlife. Species such as walruses, ringed seals, and polar bears rely on the stable ice platform for breeding, resting, and hunting. The loss of this habitat forces species to shift their distribution and migration patterns. The absence of ice also removes a natural noise dampener, leading to higher levels of ambient noise from surface waves and vessel traffic, which can interfere with the communication of marine mammals.